This invention relates generally to a multiple impingement cooled component and more particularly to a multiple impingement cooled component having improved consistency in its cooling effectiveness.
Structures, such as turbine shrouds and nozzle bands, which are subjected to high temperatures must be cooled in order to reduce possible damage caused by undesirable thermal distress and to maintain satisfactory sealing characteristics. Several methods of cooling such structures are currently being successfully employed.
One method of cooling structures is impingement cooling. In impingement cooling, air is directed to impinge substantially perpendicularly upon the surface of a structure to be cooled. When used on a turbine shroud, for example, cooling air is directed to impinge upon the back or outer surface of the shroud, that is, the surface not facing the gas flowpath. The source of the cooling air for both impingement and film cooling air in most gas turbine engines is high pressure air from the compressor. For effective impingement cooling of the entire turbine shroud in current impingement cooling arrangements, a relatively large amount of cooling air must be employed and thus the compressor must work harder to supply the cooling air. Thus, when a large amount of cooling air is required for impingement cooling, engine efficiency is reduced.
Furthermore, It is also known to incorporate multiple stages of impingement, in which cooling air is impinged through a first baffle, then accumulated and used to impinge through a second baffle, which in effect reuses the cooling air flow, lowering the overall cooling air flow requirement. However, in prior art multiple impingement designs the cooling effectiveness degrades as the cooling air flows downstream, both because of losses inherent to flow through a closed structure and because the prior art designs are not arranged so as to provide consistent impingement conditions from one stage to the next. This can lead to undesirable thermal gradients and shortened component life. Furthermore, inconsistency in cooling from one portion of a component to another can create complications when attempting to reduce cooling air flows supplied to a component to the minimum possible, because the portions of the component having the highest temperatures drive the cooling flow requirements.
Accordingly, there is a need for a multiple impingement cooled structure having improved consistency in its cooling effectiveness.
The above-mentioned need is met by the present invention, which provides a multiple impingement cooled structure having two or more stages of impingement cooling wherein the stages are arranged so as to have substantially constant cooling effectiveness.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.